1. Field of the Invention
The invention relates to a measuring system, and in particular to a system of measuring pHs of solutions and method for calibrating time-drift effects of sensors thereof.
2. Description of the Related Art
Extend Gate Ion Sensitive Field Effect Transistor (EGISFET) connects a sensing electrode, for example a titanium nitride electrode, to gate of metal oxide semiconductor field transistor (MOSFET). EGISFET can be fabricated using CMOS standard process, and is developed from Ion Sensitive Field Effect Transistor (ISFET).
Theorem and related knowledge of ISFET are detailed in the following list of documents:
1. U.S. Pat. No. 4,879,517, inventors: Connery, James G., Shaffer Jr., Earl W;
2. U.S. Pat. No. 6,617,190, inventors: Chou Jung Chuan, Chiang Jung Lung;
3. U.S. Pat. No. 5,309,085, inventor: Byung Ki Sohn;
4. U.S. Pat. No. 4,657,658, inventor: Alastair Slbbald;
5. US patent publication No. 20020180609, inventors: Kang Ding, W. E. JR. Seyfried, Zhong Zhang;
6. US patent publication No. 20030054177, inventor: Ping Jin;
7. US patent publication No. 20040075578, inventors: Olaf Dudda, Christian Oldendorf;
8. U.S. Pat. No. 4,691,167, inventors: Hendrik H. V. D. Vlekkert, Nicolaas F. de Rooy;
9. US patent publication No. 20030093011A1, inventors: Jalisi Marc Mehrzad;
10. U.S. Pat. No. 5,130,265, inventors: Massimo Battilotti, Giuseppina Mazzamurro, Matteo Giongo.
EGISFET comprises separated gate, is capable of being fabricated using CMOS standard process and has advantages of low cost, simple structure and easy package, making it suitable for biomedical application.
Many materials can act as detecting membranes for ISFETs, such as Al2O3, Si3N4, Ta2O5, amorphous WO3 (a-WO3), amorphous Si:H (a-Si:H) and others. Response time, hysteresis effect, time-drift effect, and light effect are important factors that influence performance of ISFET. EGISFET is developed from ISFET, having similar sensing principle, and therefore its performance is inevitably influenced by such non-ideal effects such as time-drift effect and hysterersis effect.